PHTN1306 Lasers III - Lab
DPSS Laser Design - Part 2 (2017F)

Introduction

In this part of the lab, the characteristics of the pump diode for the target design laser (a CST-H-473 with a single TEC which maintains the temperature of the pump diode, amplifier, and SHG at the same value) are determined. These parameters (spectrum and wavelength characteristics) will be used as the input for a convolution simulation (in the same manner as described in section 5.7 of Laser Modeling) predicting the effect of diode temperature on laser output.

Experiment:

A CST-H-473 473nm DPSS laser is connected such that the original power supply operates the pump diode at a constant current and the external ILX LDC-5910C temperature controller controls the temperature of the single TEC which sets, among other parameters, the temperature of the pump diode.

Program the LDC-5910C controller with the correct Steinhart-Hart parameters (determined experimentally) for the laser as follows:

Set the temperature for 10C and enable the temperature controller. Next, switch the "DMOH" power supply on which will operate the diode at a constant pump current. Place an 808nm bandpass filter in the path of the output beam and direct the filtered output into a fiber and then into an OSA. Adjust the fiber until the spoectrum of the pump diode is seen around 808nm.

When the temperature of the TEC has stabilized, capture the spectrum of the pump diode as well as the peak wavelength of the spectrum. The spectrum must be captured at a resolution of 0.2nm - output values will be in units of dBm which may then be converted into linear units (e.g. mW).

Now, increase the amplifier temperature to 15C and observe the peak wavelength. Repeat at a pump diode temperature of 20C, 25C,and 30C - as temperature increases we expect to see the wavelength shift to longer values.

Assignment

Hand In a WORD PROCESSED (not handwritten) lab assignment as follows. Put each question on a new page and ensure each page has a title "Question 1", "Question 2", etc. Also, please ensure the lab report is in a folder for submission (no loose pages).

To be done individually ...

  1. Submit a table of values outlining the spectrum of the pump diode at increments of 0.2nm. The table must include columns of wavelength (every 0.2nm), power observed (in dBm), power observed (normalized, in mW). The normalized power is obtained by scaling the output power so that the peak value is 1mW (0 dBm) and all other powers observed are converted into linear units and scaled accordingly.
  2. Submit a graph of peak diode wavelength (in nm) vs. diode temperature. Include an analysis: add a best-fit line and determine an equation relating wavelength to temperature in the form Wavelength(nm) = fn(Temperature).
  3. Next, complete a simulation as per discussed in the lecture. To be realistic, you will be starting with nothing more than a graph of the absorption spectrum of the material from a research paper or a laser materials manufacturer. You must digitize the graph every 0.2nm (a time-consuming, but not overtly difficult process) to produce a table of data as a starting-point. Several free utilities exist on the web to perform this digitization (e.g. CurveSnapTM or some other graph digitizer program), alternately digitization is easy using a "paint" type program which displays the X/Y coordinates of a cursor in the graphic. If, for example, it was found that there are 90 pixels between any 2nm wavelengths our required 0.2nm measurements can be taken every 9 pixels. The Y-Axis (which reflects absorption) can be calibrated in a similar manner.

    "Manual Digitization" means NO TWO STUDENTS will have the exact same results (!)

    Complete a Simulation (using the convolution technique) predicting how pump diode wavelength shift will affect Nd:YAG DPSS output based solely on absorption of the pump radiation. Assume a diode with the spectrum as determined in the last lab. Produce the following:

  4. A table of data showing the absorption of Nd:YAG vs. wavelength, every 0.2nm. You must locate an absorption curve of the material - include the source graph you located and the URL. You must digitize this graph manually or using a curve-tracer (as you would need to do with any "new" solid-state material) and so it is expected that all students will have slightly different number (that is NOT a subtle hint unless you feel the need to have a "friendly meeting" with the department chair).
  5. A printout showing the model employed. All column and row references must be visible in this picture (to do this, select an active area to print, and under the print preview menu select row/column references).
  6. A summary of the convolution formulae used: simply CUT and PASTE the formula used for the first two convoluted row cells (which will contain cell references) or present a spreadsheet printout with all formulae shown instead of values (FORMULA menu, SHOW FORMULAS option)
  7. Produce a graph showing the predicted output power (y axis) vs. the wavelength (x axis). The wavelength range required is 800nm to 810nm. On the SAME graph, show the absorption of Nd:YAG on a secondary axis so both graphs are visible.